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Eng ID Term Definition
3521
obliquity of the ecliptic
The acute angle between the plane of the ECLIPTIC and the plane of the CELESTIAL EQUATOR, about 23° 27'.
3522
obscured
(adj.). Said of the arc of a LIGHT SECTOR designated by its limiting BEARINGS in which the LIGHT is not visible from seaward.
3523
observation
The act or practice of noting and recor­ding facts and events as for some scientific study. The measure of a quantity whose value is desired... more
The act or practice of noting and recor­ding facts and events as for some scientific study. The measure of a quantity whose value is desired. The DATA so noted and recorded. A single measure, at a single setting of an ap­paratus.
3524
observation(s): astronomical
OBSERVATIONS of CELESTIAL BODIES, with appropriate instruments. In NAVIGATION, the measure­ment of ALTITUDE and AZIMUTH of CELESTIAL BODIES.
3525
observation(s): magnetic
Measurement of any of the MAGNETIC ELEMENTS.
3526
observation(s): meteorological
Evaluation or measure­ment of one or more meteorological elements.
3527
observation(s): tidal
A series of measurements taken in order to provide the information required for the REDUCTION OF SOUNDINGS, and the DATA for TIDAL PREDIC­TI... more
A series of measurements taken in order to provide the information required for the REDUCTION OF SOUNDINGS, and the DATA for TIDAL PREDIC­TION and investigation.
3528
observation equation
See EQUATION.
3529
observation spot (or pillar)
A position ashore deter­mined from celestial observations.
3530
observation tower
A tower from which one's surroun­dings can be observed, but at which a watch is not habitually maintained, as at a LOOKOUT TOWER. Such tower... more
A tower from which one's surroun­dings can be observed, but at which a watch is not habitually maintained, as at a LOOKOUT TOWER. Such towers are temporarily erected for observations in geodetic networks.
3531
observed altitude
See ALTITUDE.
3532
observed tide
Those data from tide observing equip­ment such as tide gauges, staffs, etc. "Actual tides" is an expression often used in referring to "obse... more
Those data from tide observing equip­ment such as tide gauges, staffs, etc. "Actual tides" is an expression often used in referring to "observed ti­des".
3533
obstruction
In MARINE NAVIGATION, anything that hin­ders or prevents movement, particularly anything that endangers or prevents passage of a vessel. The... more
In MARINE NAVIGATION, anything that hin­ders or prevents movement, particularly anything that endangers or prevents passage of a vessel. The term is usually used to refer to an isolated danger to NAVIGATION, such as a SUNKEN ROCK or PINNACLE.
3534
obstruction buoy
A BUOY marking an OBSTRUCTION.
3535
obstruction light
See LIGHT.
3536
occasional light
See LIGHT.
3537
occluded front
See OC­CLUSION.
3538
occlusion
Process of progressive decrease of area of warm sector at the EARTH's surface, and its ultimate disappearance, by the junction of the cold A... more
Process of progressive decrease of area of warm sector at the EARTH's surface, and its ultimate disappearance, by the junction of the cold AIR MASSES which initially precede the WARM FRONT and follow the COLD FRONT. FRONT between these two cold AIR MASSES, after their junction (also termed occluded front).
3539
occultation
The concealment or extinguishment of the light of an AID TO NAVIGATION during the dark periods of its CYCLE. In ASTRONOMY, the conceal­ment ... more
The concealment or extinguishment of the light of an AID TO NAVIGATION during the dark periods of its CYCLE. In ASTRONOMY, the conceal­ment of a CELESTIAL BODY by another which crosses the line of view. Thus, the MOON occults a STAR when it passes between the observer and the STAR.
3540
occupy
(v.t.). In SURVEYING, to observe with a surveying instrument at a STATION; also to set a surveying instrument over a point for the purpose o... more
(v.t.). In SURVEYING, to observe with a surveying instrument at a STATION; also to set a surveying instrument over a point for the purpose of making OBSERVATIONS. In OCEANOGRAPHY, to stop a ship at a selected location, an OCEANOGRAPHIC STATION, for the purpose of gathering oceanographic observations.